This invention relates generally to stripping or cleaning as is accomplished during semiconductor fabrication, such as photoresist stripping or wafer cleaning, and more particularly to mechanisms to perform such stripping and cleaning.
There are four basic operations in semiconductor processing, layering, patterning, doping, and heat treatments. Layering is the operation used to add thin layers to the surface of a semiconductor wafer. Patterning is the series of steps that results in the removal of selected portions of the layers added in layering. Doping is the process that puts specific amounts of dopants in the wafer surface through openings in the surface layers. Finally, heat treatments are the operations in which the wafer is heated and cooled to achieve specific results, where no additional material is added or removed from the wafer.
Of these four basic operations, patterning is typically the most critical. The patterning operation creates the surface parts of the devices that make up a circuit on the semiconductor wafer. The operation sets the critical dimensions of these devices. Errors during patterning can cause distorted or misplaced defects that result in changes in the electrical function of the device, as well as device defects.
The patterning process is also known by the terms photomasking, masking, photolithography, and microlithography, and involves photoresist stripping. The process is a multi-step process similar to photography or stenciling. The removal of a photoresist layer is accomplished by either wet or dry etching. Wet etching refers to the use of wet chemical processing to remove the photoresist. The chemicals are placed on the surface of the wafer, or the wafer itself is submerged in the chemicals. Dry etching refers to the use of plasma stripping, using a gas such as oxygen (O2), C2F6 and O2, or another gas. Whereas wet etching is a low-temperature process, dry etching is typically a high-temperature process.
The etching process is also referred to as stripping, such as stripping photoresist, including dry film photoresist or liquid photoresist. In wet etching, a semiconductor wafer having photoresist on it is submersed in a stripping chemical or agent and agitated to remove the photoresist. The photoresist is thus sensitive to the chemical cleaning agent. Within the prior art, the relative motion between the chemical and the semiconductor wafer is one dimensional in nature, such as in the y or z directions. FIGS. 1 and 2 show examples of how stripping, such as photoresist stripping, is current accomplished.
In FIG. 1, a side view of the system 100 includes semiconductor wafers 112 being held by a semiconductor wafer holder 110 in a vertical orientation, such as along the z direction. The holder 110, and thus the wafers 112, are submersed in a chemical solution 104 being stored in a container 102. A cylinder 106 is connected to the holder 110 via a rigid arm 108. The cylinder moves up and down in the z direction, as indicated by the arrows 114. This causes the holder 110, and thus the wafers 112, to also move up and down within the solution 104, as indicated by the arrows 116.
In FIG. 2, a top view the system 200 includes a chemical solution 204 being stored in a container 202. The semiconductor wafer 206 is moved back and forth in the y direction, as indicated by the arrows 208 and 210. Thus, the semiconductor wafer 206 goes between the position 206a and the position 206c, temporarily occupying the position 206b. The semiconductor wafer 206 is submersed in the chemical solution 204.
However, the photoresist stripping mechanisms of FIGS. 1 and 2 are disadvantageous. For instance, photoresist stripping in the context of a bump process, as this process is known within the art, may have to remove photoresist that is as thick as 120 micron. The thick photoresist is situated between the bumps in a clamped pattern, making the photoresist difficult to strip. Using the photoresist stripping mechanisms of FIGS. 1 and 2 typically leads to some photoresist residue. That is, the one-dimensional relative motion between the wafers and the chemical solution is insufficient to clean all the photoresist from the wafers, leaving photoresist residue.
Therefore, there is a need for an improved stripping mechanism that overcomes these disadvantages. Such a stripping mechanism should be useable in the context of stripping photoresist. The stripping mechanism should remove substantially all the photoresist from semiconductor wafers, even in the context of bumps, without leaving photoresist residue. For these and other reasons, there is a need for the present invention.
The invention relates to a Ferris wheel-like stripping or cleaning mechanism that can be used in semiconductor fabrication. A mechanism can include a container to hold a chemical. The mechanism can also include a component to move semiconductor wafers through the chemical in the container in a Ferris wheel-like motion. The component may include wafer holders for the wafers that are swivably mounted about an axis of rotation. As the one or more wafer holders rotate about the axis of rotation through the chemical in the container, the wafer holders remain in a substantially constant vertical and horizontal orientation.
Embodiments of the invention provide for advantages not found within the prior art. The Ferris wheel-like stripping or cleaning mechanism ensures that there is two-dimensional relative motion between the semiconductor wafers and the chemical solution. This added dimension of motion, or agitation, has been found to remove substantially all the photoresist from semiconductor wafers, even in the context of bumps, without leaving substantial photoresist residue, where the inventive mechanism is used for photoresist stripping. Where the inventive mechanism is used for cleaning polymer from a wafer after metal or via etching, it has been found that the mechanism successfully removes the polymer that even is situated in sidewalls. Still other aspects, embodiments, and advantages of the invention will become apparent by reading the detailed description that follows, and by referring to the accompanying figures.